Pilots of modern high speed aircraft such as, but not limited to, military aircraft require accurate navigation information without utilizing valuable time tracking the position of the aircraft with an unwieldy hard to read folding paper map. Moving map display systems have been developed for providing a continuous high resolution map video signal in both color and monochromatic formats to a front and center aircraft cockpit multifunction display. The map display is converted from currently available 35 mm film strips to a video output. The film strips are housed in cassettes and the moving map display automatically aligns with and tracks the present position of the aircraft. The film cassette is servo driven and contains as much as 60 feet of film corresponding to 550 square feet of maps. In order to minimize cockpit clutter, systems have been developed with a remote aircraft location capability. For a general discussion of moving map display systems reference is made to Publication 83-09-1 issued by the Flight Systems Division of the Bendix Corporation, Teterboro, N.J., 07608.
During normal operation of a moving map display system it may become necessary for the moving map to be frozen at a particular film frame or position. This occurs when the film servo slews to the next contiguous film frame as the aircraft flies off one section of the film to the next. This also occurs when, for example, an observer monitoring a secondary display needs to freeze the moving map at a particular film frame for advanced visibility or mission planning purposes, as the case may be, while the map of the primary display continues to move in accordance with its function as a navigation aid. Prior to the present invention the output display provided by the system would be blanked during the aforenoted slew and no provision was made for otherwise freezing the display for the purposes aforenoted.
In order to accommodate the above situations, the freeze frame apparatus of the invention is utilized to store (freeze) map information just prior to frame to frame slew, or at a predetermined film frame, in dynamic memory for retrieval and continuous display. When the freeze frame function is no longer required the system returns to its normal function.